Anyways, I'll just quote a Tumblr post I made about an attempt to begin poking into this issue:
Today I did some cursory research in pursuit of my question, “Can languages be diachronically transmitted from one modality to another?” So far, I know of two examples that would suggest the answer is “yes”: Damin, an instance of signed > spoken (if the author of this paper is correct), and ProTactile ASL, an instance of signed > tactile. But has there been an instance of spoken > signed?
I’m interested in Signed Exact English and related systems as a possible avenue of inquiry. SEE is often used as an educational tool to help deaf students learn English, and is often regarded as too cumbersome for everyday communication. In this way it can be thought of as equivalent to Morse Code or semaphore - an encoding of speech into a format not suitable for spontaneous conversation.
Or is it, though? A source cited by Wikipedia claims that “SEE serves as the home language for many families”. The real test of this, I suppose, would be whether SEE could be acquired natively, or used as a person’s primary or exclusive form of communication, without the person knowing (or at least not using) spoken or written English. In such a case I would expect to see some changes made to the structure of SEE, as part of natural linguistic evolution and as an adaptation to the signed modality, while remaining distinct from ASL.
I went on a deaf forum and asked if anyone there knew of any deaf/Deaf or hard of hearing people who used SEE as their primary/sole method of communication or who knew SEE without knowing spoken/written English. Many replies stated that while at some points in their life they’d used SEE (as in education), sole use of SEE wasn’t really a thing, which I what I expected to hear. However, some replies stated that they did use SEE as their primary method of communication, which was very interesting to me. One reply referenced the fact that apparently most primary-SEE users transitioned to Pidgin Signed English, to cut down on the clunkiness of SEE.
Now, what is Pidgin Signed English? Wikipedia says that the term refers to the different contact languages that arise between English and any of BSL, NZSL, Auslan or ASL - so, a pidgin. This website says PSE is a combination of ASL and English (sounds like a pidgin) - but then it says “With PSE, someone might sign most of the English words of a sentence and use approximately the English syntax.” That doesn’t sound like a pidgin. That sounds like a variety of English, particularly if the signs in question are from SEE. It also sounds a lot like the streamlined version of SEE one user on the forum mentioned, who equated it with PSE.
I suppose I ought to find some research about PSE. I’m guessing that what people call “PSE” is actually not really one thing, encompassing both pidgin combinations of ASL and English and “streamlined” versions of SEE. And the variety of “streamlined” SEE apparently used by these primary-PSE users might just be the adapted-to-the-signed-modality variety of English I’m looking for.